Philosophy of Physical Magnitudes

Dimensional quantities such as length mass and charge i.e. numbers combined with a conventional unit are essential components of theories in the sciences especially physics chemistry and biology. Do they represent a world with absolute physical magnitudes or are they merely magnitude ratios in disguise? Would we notice a difference if all the distances or charges in the world suddenly doubled? These central questions of this Element are illustrated by imagining how one would convey the meaning of a kilogram to aliens if one were only allowed to communicate via Morse code.